1. Field of the Invention
The present invention relates to a heat pump system for a vehicle, and more particularly, to a heat pump system for a vehicle that includes: a water-cooled type heat exchanger, which is a heat supply means, mounted on a first bypass line, which bypasses a second indoor heat exchanger (evaporator), for collecting waste heat of vehicle electric devices; a branch line for connecting a refrigerant circulation line of the second indoor heat exchanger and the first bypass line with each other; and a second bypass line, which bypasses an outdoor heat exchanger.
2. Background Art
An air conditioner for a vehicle generally includes a cooling system for cooling the inside of the vehicle and a heating system for heating the inside of the vehicle. The cooling system exchanges heat between air, which passes through the outside of an evaporator near the evaporator of a refrigerant cycle, and refrigerant, which flows inside the evaporator, to thereby change the air into cold air, so that the cooling system can cool the inside of the vehicle. The heating system exchanges heat between air, which passes near the outside of a heater core of a cooling water cycle, and cooling water, which flows inside the heater core, to thereby change the air into warm air, so that the cooling system can heat the inside of the vehicle.
In the meantime, differently from the air conditioner for the vehicle, but a heat pump system that selectively carries out cooling and heating by converting a flow direction of refrigerant using one refrigerant, cycle is applied to the vehicle. For instance, the heat pump system includes two heat exchangers: one being an indoor heat exchanger mounted inside an air-conditioning case to carry out heat-exchange with air blown to the inside of the vehicle; and the other being an outdoor heat exchanger mounted outside the air-conditioning case to carry out heat-exchange, and a direction-switching valve which can convert a flow direction of refrigerant.
Accordingly, in the case that a cooling mode is operated according to the flow direction of refrigerant by the direction-switching valve, the indoor heat exchanger serves as a heat exchanger for cooling, but in the case that a heating mode is operated, the indoor heat exchanger serves as a heat exchanger for heating.
There are various kinds of heat pump systems for vehicles, and FIG. 1 illustrates an example of the heat pump systems.
The heat pump system for a vehicle illustrated in FIG. 1 includes: a compressor 30 for compressing and discharging refrigerant; a high pressure heat exchanger 32 for radiating heat of the refrigerant discharged from the compressor 30; a first expansion valve 34 and a first bypass valve 36, which are mounted in parallel and selectively passes the refrigerant passing through the high pressure heat exchanger 32; an outdoor unit 48 for heat-exchanging the refrigerant, which passes through the first expansion valve 34 or the first bypass valve 36, outdoors; a low pressure heat exchanger 60 for evaporating the refrigerant that passes through the outdoor unit 48; an accumulator 62 for dividing the refrigerant, which passé through the low pressure heat exchanger 60, into a gas phase and a liquid phase; an indoor heat exchanger 50 for exchanging heat between refrigerant supplied to the low pressure heat exchanger 60 and refrigerant returning to the compressor 30; a second expansion valve 56 for selectively expanding the refrigerant supplied to the low pressure heat exchanger 60; and a second bypass valve 58 mounted in parallel with the second expansion valve 56 for selectively connecting an outlet of the outdoor unit 48 with an inlet of the accumulator 62.
In FIG. 1, the reference numeral 10 designates an air-conditioning case having the high pressure heat exchanger 32 and the low pressure heat exchanger 60 therein, the reference numeral designates a temperature control door for controlling an amount of mixing between cold air and warm air, and the reference numeral 20 designates an air blower mounted at an inlet of the air-conditioning case.
In the conventional heat pump system for the vehicle having the above structure, when a heat pump mode (heating mode) is operated, the first bypass valve 36 and the second expansion valve 56 are closed but the first expansion valve 34 and the second bypass valve 58 are opened.
Moreover, the temperature control door 12 is actuated as shown in FIG. 1. Accordingly, the refrigerant discharged from the compressor 30 passes through the high pressure heat exchanger 32, the first expansion valve 34, the outdoor unit 48, a high pressure part 52 of the indoor heat exchanger 50, the second bypass valve 58, the accumulator 62, and a low pressure part 54 of the indoor heat exchanger 50 in order, and then, is returned to the compressor 30.
That is, the high pressure heat exchanger 32 serves as a heater and the outdoor unit 48 serves as an evaporator.
When an air-conditioning mode (cooling mode) is operated, the first bypass valve 36 and the second expansion valve 56 are opened, but the first expansion valve 34 and the second bypass valve 58 are closed. Furthermore, the temperature control door 12 closes a passage of the high pressure heat exchanger 32.
Accordingly, the refrigerant discharged from the compressor 30 passes through the high pressure heat exchanger 32, the first bypass valve 36, the outdoor unit 48, the high pressure part of the indoor heat exchanger 50, the second expansion valve 56, the low pressure heat exchanger 60, the accumulator 62, and the low pressure part 54 of the indoor heat exchanger 50 in order, and then, is returned to the compressor 30.
That is, the low pressure heat exchanger 60 serves as the evaporator and the high pressure heat exchanger 32 closed by the temperature control door 12 serves as the heater like in the heat pump mode.
However, in the heat pump mode (heating mode) of the conventional heat pump system for the vehicle, the high pressure heat exchanger 32 mounted inside the air-conditioning case 10 carries out heating as the heater and the outdoor unit 48 mounted outside the air-conditioning case 10, namely, in front of the engine room of the vehicle, serves as the evaporator to exchange heat with the outdoor air.
In this instance, when the outdoor temperature is low, the outdoor unit 48 serving as the evaporator cannot supply sufficient waste heat to the high pressure heat exchanger 32 serving as the heater because exchanging heat with the outdoor cold air. If a heat source is not secured in the condition that the outdoor temperature is low, the heating performance is deteriorated, and particularly, heat-exchange efficiency between refrigerant and the outdoor air is decreased due to a frost accumulation of the outdoor unit 48, so that the heating performance and the efficiency of the heat pump system are reduced.
Furthermore, in order to solve the problem of degradation of performance in the condition that the outdoor temperature is low, there is an attempt to install an electric heater (not shown) inside the air-conditioning case 10 as a main heating device or an auxiliary heating device, but in the case that the electric heater is used as the heating device, because there is a limit in electric energy to be supplied to an electric vehicle or a fuel cell vehicle, the conventional heat pump system for the vehicle has a problem in that a mileage of the vehicle by a battery drops sharply due to an excessive power consumption by the operation of the electric heater.